Field of Invention
The present invention relates to a work piece having an electroplating layer on its surface and a method for manufacturing the same, in particular, to a nickel and/or chromium plated member or a method for manufacturing the same.
Related Art
The environmentally friendly requirements are stricter and stricter in the European market and the demands of corrosion resistance for electroplating in main engine plants are higher and higher. At present trivalent chromium electroplating could not meet the corrosion requirements for some special environment, that is to say, could not be subject to the Copper-Accelerated Acetic Acid-Salt Spray Testing for 80 hours and the Russian mud resistance test for 336 hours.
The anti-corrosive capacity of a work piece could be improved by plating two or three layers of nickel and then plating chromium in the electroplating industry. The widely applied two-layer nickel plating process includes plating Semi-bright nickel, bright nickel, and crack-free chromium. The widely applied three-layer nickel plating process includes plating Semi-bright nickel, bright nickel, microporous nickel, and crack-free chromium or plating Semi-bright nickel, bright nickel, micro-crack nickel, and crack-free chromium. However, as the stress of the chromium layer itself is large, it is difficult to obtain a chromium plating layer without any cracks or pores in the industry, including a hexavalent chromium and a trivalent chromium plating layer. When the chromium plating layer exposed to the air is passivated, its potential is more positive than that of nickel. And the chromium plating layer will form a corrosion cell with the nickel layer when it encounters the corrosion medium. Consequently, the decorative nickel plating layer will be irregularly corroded to a large extent in extreme environments, and the chromium player may fall off due to large-area corrosion of the nickel layer. In order to further improve the anti-corrosive capacity of the nickel layer, microporous nickel and micro-crack nickel are applied to the bright nickel plating layer. A special high stress nickel layer is plated on the bright nickel layer by using micro-crack nickel and a large number of micro-cracks will be generated by the stress after chromium is plated. The microporous nickel layer diverges the corrosion current in the multi-layer nickel to prevent forming corrosion points in depth and avoid, visible corrosion. As the micro-crack nickel layer is separately used, the fog will be produced on the surface of the product, the brightness thereof is poor, and the trivalent chromium plating is not involved. Additionally, the microporous nickel or micro-crack nickel is separately used, resulting in a limited improvement in anti-corrosive capacity. Moreover, it is disclosed in a part of the prior art that the feature for noble potential is achieved by altering the microporous nickel process to meet the requirement for anti-corrosive performance of trivalent chromium. However, the noble potential microporous nickel could not be matched well with hexavalent chromium to satisfy anti-corrosive demands.
In the prior art, for example in Chinese Patent Publication No. 101988211, multi-layer nickel plating process for metal surface having a good anti-corrosive feature is disclosed. The plating process includes (A) to metalize the surface of to plastic piece, (B) to plate bright copper, (C) to plate Semi-bright nickel, (D) to plate high sulfur nickel, (E) to plate bright nickel, (F) to plate microporous nickel, (G) to wash by water, (H) to plate bright chromium, (I) to wash by water, and (J) to dry. Even though the anti-corrosive performance of the plastic piece is enhanced slightly by using four layers of nickel-nickel electroplating solution for plating on the surface of the plastic, the anti-corrosive capacity of the said process could still not meet the requirement for corrosion environment containing deicing salt (CaCl2). Fog could be formed partly on the high sulfur nickel electroplating layer. Moreover, the plastic surface treatment is not adequate in this process, bringing poor deep plating capacity to the plating layer and causing the plating layer easily crisp. The plastic subject to electroplating treatment has a short use life as members for vehicles, for example grills, decorative bars and door handles. The introduction to the process for micro-crack nickel is made in Chinese Patent Publication No. 101705508A, which discloses electroplating solution for micro-crack nickel plating and its application. The main components of the micro-crack nickel electroplating solution include 180˜260 g/L of nickel chloride, 20˜60 ml/L of acetic acid, 80˜120 ml/L of ELPELYT MR and 1˜5 ml/L of 62 A. The description of embodiments of the patent document is limited to hexavalent chromium plating and trivalent chromium plating is not mentioned therein.